This application is based on patent applications Hei.11-166919 and Hei.11-185197 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
This invention relates to an actuator, such as a truss type actuator for generating an elliptic movement of a driven object by composition of displacements of a plurality of displacing devices where the displacing devices are driven by using resonance phenomenon, and methods for driving the actuator.
2. Description of the Related Art
A first conventional truss type actuator is shown in xe2x80x9cDevelopment of a Small Actuator with Three Degrees of Rotational Freedom (1st Report)xe2x80x9d by K. SASAE et. al., Journal of Precision Engineering Institution, Vol.61, No.31, 1995. In the first conventional actuator, a chip member is provided at a crossing point of three lamination type piezoelectric devices. The piezoelectric devices are driven for moving the chip member so as to trail a spherical surface, so that a spherical driven member can be revolved in an optional direction. Since the piezoelectric devices are driven in non-resonance mode, the displacement of the piezoelectric devices are not so large and the driving efficiency of the actuator is relatively low.
A second conventional truss type actuator is shown in xe2x80x9cManufacture and Estimation of Thin Ultrasonic Linear Motorxe2x80x9d by S. NAGATOME, et. al., Collection of Lecture of Precision Engineering Institution, in Spring, 1998. In the second conventional actuator, a steel plate is blanked so that two displacing portions cross at a right angle. Piezoelectric devices are fixed on respective displacing portions. One of the piezoelectric device is resonantly driven for colliding the peak at the crossing point of the displacing portions with a driven member obliquely. Thus, the driven member is moved in a predetermined direction. Since the piezoelectric device is driven in resonance mode, the displacement of the piezoelectric device can be made larger. The peak of the steel plate, however, collides with the driven member linearly, so that acoustic noise and vibrations of the actuator are relatively larger. Furthermore, the steel plate and the driven member are heavily worn. Also, the actuator has no mechanism for detecting the displacement of the piezoelectric device, so that it is difficult to control the moving speed of the driven member.
A third conventional traveling wave type actuator is shown in the publication of xe2x80x9cAdmission into Ultrasonic Motorxe2x80x9d by Sogo Denshi Shuppansha Japan. In the third conventional actuator, a plurality of piezoelectric devices are adhered on a circular elastic member at a predetermined interval. When the elastic member is resonantly vibrated by driving the piezoelectric devices, traveling waves are formed in a direction parallel to an axis of the circular elastic member. A driven member disposed on the circular elastic member can be rotated around the axis of the circular elastic member. Since the elastic member and the driven member are shaped to be circular, freedom for designing an apparatus using the actuator becomes narrower.
A fourth conventional linear actuator is shown in xe2x80x9cFirst Report of Piezoelectric Traveling Wave type Linear Actuatorxe2x80x9d by H. OKU, et. al., Collection of Lecture of Precision Engineering Institution, in Spring, 1995. In the fourth conventional actuator, a plurality of piezoelectric devices are adhered on a side wall of an endless elastic member. Each piezoelectric device is driven by two kinds of the natural vibration modes, and the displacements of the vibrations of the piezoelectric devices are compounded so as to generate the traveling waves on the surface of the elastic member and parallel to the endless section of the elastic member. Since the whole of the elastic member is vibrated, a mass of an object to be vibrated by the piezoelectric devices becomes larger. Thus, the frequencies of the driving signals for driving the piezoelectric device become smaller, and an output of the actuator become smaller. Furthermore, it is difficult not only to control the condition for resonantly vibrating the elastic member but also to connect the elastic member. Also, since the deformation of the elastic member is complex, it is difficult to control the condition to obtain a desired elliptic movement.
An object of this invention is to provide an actuator having a simple configuration and high driving efficiency, which can easily be controlled.
An actuator in accordance with an aspect of this invention comprises a plurality of displacing devices for generating displacements; a compound member connected to the displacing devices and for compounding displacements of the displacing devices; a base member for folding base ends of the displacing devices at which the compound member is not connected; a pressing member for pressing the compound member to an object to be driven; and a driver for resonantly driving the displacing devices so as to move the compound member an elliptic or a circular trail.
By the above-mentioned configuration, the displacing devices are resonantly driven, so that the displacements of the displacing devices are enlarged. Thus, the driving efficiency of the actuator can be increased.